This section describes the overall end-to-end protocol structure of Evolved UMTS for the User and Control planes, which correspond respectively to user data transmission and signalling transmission.
From the wireless network perspective – including both Access and Core parts – the User plane not only includes user data such as voice packets or Web content, but also the signalling associated to the application services such as the SIP or RTCP, which are described further in this chapter. Although being considered as control information by the application layers, the high-level signalling is transmitted via the User plane.
The end-to-end User plane is described in Figure 4.6, from the terminal up to the application server. In this picture, the application layer, only present in the terminal and application server, is based on an IP transport. The application-level packets are routed through Packet Core Gateways before reaching the destination. In this example, the application layer may comprise a very large set of protocol-like end-to-end transport protocols (e.g. TCP or UDP) and RTP (Real Time Protocol) for user data transport, as well as application-level signalling protocols mentioned above (SIP, SDP, RTCP, etc.). Further, in this chapter, a section dedicated to IMS protocol stack describes the set of ‘application-level’ protocols which can be used to support IMS-based services.
In this picture, L1 and L2 refer respectively ...